Datasheet: I2782A-08TR (Alliance Semiconductor Corporation)

Notice: The information in this document is subject to change without notice.

General Purpose EMI Reduction IC

Features

Provides up to 15dB of EMI suppression

FCC approved method of EMI attenuation

Generates a 1X, 2X, and 4X low EMI spread

spectrum clock of the input frequency

Input frequency range from 3 to 78MHz

External loop filter for spread % adjustment

Spreading ranges from ±0.25% to ±5.0%

Ultra low cycle-to-cycle jitter

Zero-cycle slip

3.3V operating voltage range

10 mA output drives

TTL or CMOS compatible outputs

Ultra-low power CMOS design

P278XA is available in 8 pin SOIC and TSSOP

Packages

Available for industrial and automotive

temperature ranges.

Product Description

The P278xA is a versatile spread spectrum frequency modulator designed specifically for digital camera and

other digital video and imaging applications. The P278xA reduces electromagnetic interference (EMI) at the clock source, which provides system wide reduction of EMI of all clock dependent signals. The P278xA allows significant system cost savings by reducing the number of circuit board layers and shielding that are traditionally required to pass EMI regulations.

The P278xA uses the most efficient and optimized modulation profile approved by the FCC. The P278xA modulates the output of a single PLL in order to "spread" the bandwidth of a synthesized clock and, more importantly, decreases the peak amplitudes of its harmonics. This results in significantly lower system EMI compared to the typical narrow band signal produced by oscillators and most frequency generators. Lowering EMI by increasing a signal's bandwidth is called spread spectrum clock generation.

Notice: The information in this document is subject to change without notice.

Loop Filter Selection Table VDD 3.3V

Contact Alliance for loop values that are not listed in the table and for component selection values for industrial and automotive temperatures.

BW = ±0.50%

1

BW = ±0.75%

1

BW = ±1.00%

1

BW = ±1.25%

1

Input

MHz

FS1 FS0

C1

(pF)

C2

(pF)

R1

(ohm)

C1

(pF)

C2

(pF)

R1

(ohm)

C1

(pF)

C2

(pF)

R1

(ohm)

C1

(pF)

C2

(pF)

R1

(ohm)

3

0 0 270 330,000 220 270 330,000

300 270 100,000

390 560 100,000

510

4

0 0 270 100,000 270 270 100,000

390 270 100,000

560 560 100,000

680

5

0 0 270 100,000 390 270 100,000

560 270 100,000

750 560 100,000

910

6

0 0 270 100,000 510 270 100,000

750 270 10,000 1,000 680

6,800

1,200

7

0 0 270 100,000 620 270 100,000 1,000

270 5,600 1,200 330

3,300

1,200

8

0 0 270 100,000 820 270 100,000 1,200

270 12,000 2,200 680

6,800

2,200

9

0 0 270 100,000 1,000 270 100,000 1,500

270 5,600 2,200 270

2,700

2,200

10 0 1 270 100,000 330 270 100,000

510 270 100,000

750 560 100,000

910

11 0 1 270 100,000 390 270 100,000

560 270 100,000 866(1%)

560 100,000

1,100

12 0 1 270 100,000 510 270 100,000

750 270 10,000 1,000 680

6,800

1,200

13 0 1 270 100,000 560 270 100,000

820 270 12,000 1,200 470

4,700

1,200

14 0 1 270 100,000 620 270 100,000 1,000

270 5,600 1,200 330

3,300

1,200

15 0 1 270 100,000 750 270 100,000 1,100

270 3,900 1,200 330

3,300

1,500

16 0 1 270 100,000 820 270 100,000 1,200

270 12,000 2,200 680

6,800

2,200

17 0 1 270 100,000 910 270 100,000 1,300

270 10,000 2,200 390

3,900

2,200

18 0 1 270 100,000 1,000 270 100,000 1,500

270 5,600 2,200 270

2,700

2,200

19 0 1 270 100,000 1,200 270 100,000 1,600

270 3,300 2,200 270

2,700

2,700

20 0 0 270 100,000 330 270 100,000

560 270 100,000

750 560 100,000

910

21-22 1 0 270 100,000 390 270 100,000

620 270 100,000 866

(1%) 560 100,000

1,100

23-24 1 0 270 100,000 510 270 100,000

750 270 10,000 1,000 680

6,800

1,200

25-26 1 0 270 100,000 560 270 100,000

820 270 12,000 1,200 470

4,700

1,200

27-28 1 0 270 100,000 620 270 100,000 1,000

270 6,800 1,200 330

3,300

1,200

29-30 1 0 270 100,000 750 270 100,000 1,100

270 3,900 1,200 330

3,300

1,500

31-32 1 0 270 100,000 820 270 100,000 1,200

270 12,000 2,200 680

6,800

2,200

33-34 1 0 270 100,000 910 270 100,000 1,300

270 10,000 2,200 390

3,900

2,200

35-36 1 0 270 100,000 1,000 270 100,000 1,500

270 5,600 2,200 270

2,700

2,200

37-38 1 0 270 100,000 1,200 270 100,000 1,600

270 3,300 2,200 270

2,700

2,700

39-42 1 1 270 100,000 330 270 100,000

560 270 100,000

750 560 100,000

910

43-46 1 1 270 100,000 390 270 100,000

620 270 100,000 866

(1%) 560 100,000

1,100

47-50 1 1 270 100,000 510 270 100,000

750 270 10,000 1,000 680

6,800

1,200

51-54 1 1 270 100,000 560 270 100,000

820 270 12,000 1,200 470

4,700

1,200

55-58 1 1 270 100,000 620 270 100,000 1,000

270 6,800 1,200 330

3,300

1,200

59-62 1 1 270 100,000 750 270 100,000 1,100

270 3,900 1,200 330

3,300

1,500

63-66 1 1 270 100,000 820 270 100,000 1,200

270 12,000 2,200 680

6,800

2,200

67-70 1 1 270 100,000 910 270 100,000 1,300

270 8,200 2,200 390

3,900

2,200

71-74 1 1 270 100,000 1,000 270 100,000 1,600

270 5,600 2,200 270

2,700

2,200

75-78 1 1 270 100,000 1,200 270 100,000 1,800

270 3,300 2,200 270

2,700

2,700

1 The BW value is representative of typical conditions

July 2005

P2781/82/84

rev 1.5

General Purpose EMI Reduction IC

4 of 11

Notice: The information in this document is subject to change without notice.

Spread Spectrum Selection

The P278xA performs Zero Cycle Slip when set at low percentage spreading. This allows no occurrence of system timing error. The optimal setting should minimize system EMI to the fullest without affecting system performance. The spreading is described as a percentage deviation of the center frequency. (Note: the center frequency is the frequency of the external reference input on CLKIN, Pin 1.)

The P2781A is designed for PC peripheral, networking, notebook PC, and LCD monitor applications. It is optimized for operation between 3 to 78MHz range. In the following application schematic example, the P2781A spread percentage selection is determined by the external LF value specified in the Loop Filter Selection Table. The Input Frequency Selection Table specifies the input frequency range. The external LF allows the user to fine tune the spread percentage to optimize the EMI reduction benefits of the spread spectrum.

Note: Both logic input pins FS1 and FS0 have to be connected to either VDD or VSS. Do not leave them floating.

1

2

3

4

8

7

6

5

VDD

FS0

ModOUT

VSS

LF

FS1

XOUT

XIN/CLKIN

P2781A

+3.3V

Modulated 16MHz Clock To target Chip

16 MHz

0.1µF

C2 C1

R1

0 Ohm

2.2 K

July 2005

P2781/82/84

rev 1.5

General Purpose EMI Reduction IC

5 of 11

Notice: The information in this document is subject to change without notice.